1. Field of the Invention
The present invention relates to a plasma processing method, particularly, to a plasma processing method in which organic materials such as a photoresist film remaining on the surface of the target object to be processed after, for example, the etching process is removed by using plasma and also relates to a plasma processing apparatus used for working the plasma processing method.
2. Description of the Related Art
In various semiconductor devices, the miniaturization and multi-layered construction of the wiring structure are being promoted in accordance with the progress in the degree of integration that has been achieved in recent years. Since the miniaturization of the wiring structure tends to invite an increase in the capacitance between adjacent wirings, a low dielectric constant material (low-k material) has come to be used for forming an interlayer insulating film. In, for example, the technology known to the art as the damascene process, a wiring groove is formed by selectively etching an interlayer insulating film, followed by burying Cu having a low resistivity in the wiring groove thus formed and subsequently planarizing the interlayer insulating film by a CMP (Chemical Mechanical Polishing) treatment so as to form a wiring. A low-k material such as a SiOCH series material is used for forming the interlayer insulating film.
In the manufacturing process of a semiconductor device, an etching treatment utilizing the photolithography technology is carried out for forming a device structure. For example, in the damascene process referred to above, a photoresist film formed on the interlayer insulating film is patterned and, then, the interlayer insulating film is subjected to an etching treatment by using the patterned photoresist film as a mask so as to form a wiring groove in the interlayer insulating film. Further, the remaining photoresist film is removed by an ashing process. The ashing process can be carried out by a plasma processing using, for example, an oxygen gas plasma. However, it is known to the art that the low-k material tends to incur a so-called “plasma damage” that the low-k material is affected by the plasma in performing the ashing process, with the result that the low-k material is oxidized and denatured. For example, if the interlayer insulating film incurs the plasma damage, various problems are generated. First of all, in the subsequent washing process with a dilute hydrofluoric acid (HF), the denatured portion of the interlayer insulating film is dropped so as to bring about a change in the shape of the etched portion. An additional problem is that the film quality is lowered so as to elevate the dielectric constant. As a result, the wiring capacitance is increased, and a delay of signal is invited.
Under the circumstances, Japanese Patent Application Kokai Publication No. 2000-183040 proposes a method that a hole is formed first by etching in an organic interlayer insulating film, then, an underlying substance is allowed to be attached to the side wall of the hole by performing a reverse sputtering in order to prevent the organic interlayer insulating film from being denatured or changed in shape by the ashing treatment in the subsequent step, followed by performing a plasma processing.
Also, Japanese Patent Application Kokai Publication No. 7-211492 proposes a method of carrying out a plasma ashing treatment by using a mixed gas consisting of oxygen and a rare gas and having a pressure of 100 Torr in order to prevent the damage caused by the function of ions in the ashing stage, though the technology disclosed in this prior art is not directed to a low-k film such as a SiOCH series film.
However, in the method disclosed in Japanese Patent Application Kokai Publication No. 2000-183040 quoted above, it is necessary to employ a new additional step of the reverse sputtering process in order to suppress the plasma damage, leading to the demerit that the number of process steps is increased. In addition, the conditions themselves of the ashing treatment have not yet been studied.
In the method disclosed in Japanese Patent Application Kokai Publication No. 7-211492 quoted above, the processing is carried out under a relatively high pressure close to the ordinary pressure in order to suppress the damage done by ions. Naturally, it is impossible to apply the method disclosed in the patent document quoted above as it is to the ordinary plasma ashing process that is carried out under the state close to the state of vacuum (e.g., to the ashing process disclosed in Japanese Patent Application Kokai Publication No. 2000-183040 quoted above).
As pointed out above, the prior art was not satisfactory in the aspect that the plasma damage done to the low-k film such as a SiOCH series film is suppressed by controlling the conditions of the ashing treatment.